1. Field of the Invention
The present invention relates to a structure for supporting a sample to be subjected to surface enhanced vibrational spectroscopic analysis and a method of manufacturing the structure, and more particularly, to a jig for surface enhanced vibrational spectroscopic analysis which is used for Raman spectroscopic analysis or infrared spectroscopic analysis and a method of manufacturing the jig.
2. Description of the Related Art
When a sample is irradiated with laser light, Raman scattered light which is different in frequency from original incident light is emitted from the sample together with Rayleigh scattered light which is equal in frequency to the original incident light. A Raman spectroscopic analysis method of analyzing the Raman scattered light is effective to determine a molecular structure or a bonding state of crystal.
However, there is a case where a sample such as an organic substance is sensitive to damage by laser light, so it is necessary to measure the sample at minimum laser intensity. Because the Raman scattered light intensity is extremely weak, when the sample is a thin film or when a measurement area is very small, it may be difficult to obtain the Raman spectrum. Therefore, there is required a technique for detecting the Raman scattered light whose intensity is extremely weak at high sensitivity even when the sample is irradiated with laser light at an intensity level at which the sample is not damaged.
An example of such technique is surface enhanced Raman scattering (SERS) (see Chem. Phys. Lett., Vol. 126, p. 163 (1974)). The SERS is a phenomenon in which the intensity of Raman scattered light from a sample of a monomolecular layer or a several-molecular layer which is deposited on a substrate on which a metal film made of a noble metal such as silver, gold, or copper (island-like film or fine particle film) is formed is 102 to 106 times larger than the intensity of Raman scattered light from a sample deposited on a substrate on which the metal film is not formed. It is also necessary to make the surface of the metal film rough. For example, a film which contains Si particles, Ag particles, or CaF2 having a μm-size is formed as a ground film. When the metal film is formed on the ground film, the roughness of the surface of the metal film increases, so the SERS is observed at higher sensitivity (see J. Phys. Chem. 1985, 89, 5174-5178, and Solid State Communications, Vol. 55, No. 12, pp. 1085-1088, 1985). Even when the metal film is deposited on the surface of the sample, the SERS phenomenon is observed.
The same is expected even in the case of an infrared spectroscopic analysis method. When the sample is irradiated with infrared light, an infrared light having a frequency peculiar to the sample is absorbed thereinto. Information with respect to the molecular structure or environments of the molecules is obtained based on a frequency at an absorption position.
In recent years, a scanning probe microscope, a near-field microscope, an atomic force microscope, and the like have been under development. Therefore, the structure of each metal nano fine particle can be measured in nanoscale and simultaneously an interparticle distance can be controlled to detect Raman scattered light only from a specific particle to which an extremely small amount of molecules are absorbed. For example, according to J. Phys. Chem. B, 2003, 107, 7607-7617, it has been reported that a local electric field intensity on the surface of a nano structure when the metal nano structure which produces sufficient SERS is irradiated with laser light is obtained by numeral calculation, thereby finding the metal nano structure which provides a very large enhanced intensity. When a local electric field intensity on an isolated spherical or elliptical metal nano particle is calculated, only an SERS enhanced intensity of 104 to 105 is obtained. In contrast to this, an enhanced intensity of 1010 or more which is equivalent to the sensitivity for a single molecule is obtained on a bonding area between spherical or elliptical nano particles at a suitable wavelength without depending on particle size. In other words, it is reported that the very large enhanced intensity equivalent to the sensitivity for a single molecule is obtained on the aggregation of the metal nano particles and the bonded particles.
It has been known that a structure in which metal fine particles are brought close to each other or bonded to each other is used for spectroscopic analysis of surface enhanced Raman scattering. For example, a metal is put into fine holes and exposed to shorten a distance between respective exposed metal fine particles to several nm. An analysis sample is deposited to the surfaces of the exposed metal fine particles and then irradiated with laser light. Therefore, surface enhanced Raman scattering measurement using an electromagnetic field generated between the metal fine particles to improve the sensitivity can be performed (see US 2005/0105085).
According to the conventional vibrational spectroscopic analysis method using the surface enhanced phenomenon, a Raman scattered light intensity or an absorption intensity is increased corresponding to an adsorption state of the sample on the metal film or an adsorption state of a metal on the surface of the sample. However, there is a problem that, when the sample is irradiated with incident light whose intensity is small, Raman scattered light of the sample or infrared absorption thereof cannot be measured in some cases.
It has been reported that a sufficient SERS intensity is obtained from a bonding area of an aggregate of metal nano particles and the vicinity thereof, or the like. In particular, in order to obtain the sufficient SERS intensity using metal nanostructures such as particles, the following is required. That is, the metal nanostructures are aggregated in high density or the metal nanostructures are disposed at an interval of approximately 0 nm to several nm (see US 2005/0105085). However, US 2005/0105085 describes that the metal nanostructures are only two-dimensionally disposed. In order to obtain the SERS intensity at high sensitivity, it is necessary to increase a surface area of a metal to which a measurement sample is deposited or the number of metal fine particles.